1. Field of the Invention
The present invention relates to seed meters for dispensing individual seeds at a controlled rate into a seed furrow as the seed meter is advanced along the furrow, and more particularly to air seed meters in which a rotating element coupled to a source of air pressure or vacuum picks up individual seeds from a seed mass and subsequently discharges the seeds therefrom in controlled fashion as the element continuously rotates.
2. History of the Prior Art
Seed meters of various designs have been employed to dispense seeds at a controlled rate into a seed furrow a the seed meter is advanced along the furrow. In a typical arrangement a tractor is coupled to tow a tool bar to which are attached in generally parallel, spaced apart relation a plurality of planting units with seed meter arrangements attached thereto. Each of the planting units includes a seed hopper for containing a quantity of the seed to be planted, a device for opening a furrow as the tractor drawn tool bar is advanced over the ground, a seed meter coupled to the seed hopper for dispensing individual seeds into the furrow at a controlled rate and a further device for moving soil at the sides of the furrow to close the furrow over the seeds. The planting unit may further include containers for insecticide and fertilizer together with apparatus for dispensing controlled amounts of each.
Planting arrangements of the type described typically have apparatus including rotatable wheels in contact with the ground or other distance monitoring devices for controlling the rate of discharge of seeds from the seed meter so that the proper seed spacing is achieved. The tractor typically moves across the ground at a speed of 4-8 miles per hour. The spacing between individual seeds in each furrow can range from as little as 0.6 inch or less to as much as 15 inches or more depending upon the type of seeds being planted. The seed meters must accordingly be capable of dispensing seeds at a very high rate on the order of 200 seeds per second or greater as well as at rates which are considerably lower. The many different types of seeds which are typically planted in this fashion include corn, cotton, sorghum, sugar beets, soy beans and sunflower. Such seeds vary considerably in both size and shape. For example, corn seeds are among the largest and have an irregular surface. Soy bean, cotton and sunflower seeds are slightly smaller an tend to be rounded, elongated and very elongated in shape, respectively. Sorghum and sugar beet seeds are still smaller and generally spherical, the former having a relatively smooth outer surface and the latter having a very rough and irregular outer surface. Despite such differences in size and shape, seed meters are expected or required to handle two or more or even all of the different types of seeds described with a minimum of part changes and adjustments. At the same time required standards of planting accuracy typically require a low error rate. A missed seed or a doubling of seeds is undesirable and may be allowed only very infrequently. Such requirements place considerable demands upon the accuracy of the seed meters.
Some seed meters used in planting arrangements of the type discussed are of the mechanical type in which mechanically actuated fingers or similar mechanical devices are typically used to separate individual seeds from a seed mass and then dispense them into the furrow. While mechanical seed meters are satisfactory for certain applications, they typically suffer from a number of limitations which include a limitation in the speed at which they can accurately dispense seeds, an inability to handle different types of seeds without making cumbersome and extensive part changes, and an inherent design complexity which may typically add to the cost, wear and maintenance problems of the seed meters.
An alternative type of seed meter which uses an air pressure differential has been developed in an effort to overcome some of the problems of mechanical seed meters. Air pressure differential seed meters, which are commonly known as air seed meters are generally of two types, the first being the positive pressure type and the second being the vacuum type.
In the positive pressure type of air seed meter, air is blown into the seed chamber and onto the surface of a rotating or otherwise movable member in order to create a higher than atmospheric pressure in the chamber. This forces seeds from a seed mass onto the member where they are retained for later release. The rotating member is typically provided with apertures open to atmosphere where the individual seeds are held by the blowing air until the seeds are dispensed by interrupting the flow of air to the seeds.
Examples of positive pressure type air seed meters are provided by U.S. Pat. Nos. 3,888,387 of Deckler, 4,047,638 of Harrer and 4,074,830 of Adams. In the Deckler patent pressure is applied to a disk having irregularly shaped pockets for the seeds and radial passages for air flow. A separate pressure gate is employed to help eliminate excess seeds and to discharge the seeds from the disk. In the Harrer patent pressure is applied to a disk having clamshell-shaped pockets in which the individual seeds are held by the pressure differential until discharge by passage of the disk through a region that is isolated from the pressurized air. In the Adams patent pressurized air is also applied to a disk having seed-carrying pockets. Once the seed is in the pocket, the pockets contact a flat sealing surface to hold the seeds in the pockets until discharge is desired. Still other patents which relate to this type of arrangement include U.S. Pat. No. 3,999,690 of Deckler which describes a stainless steel wear plate driven by the metering disk and which is wear resistant, and U.S. Pat. No. 4,091,964 of Harrer which describes in further detail a sealing pad for use in the arrangement of the Adams patent.
While air seed meters of the positive pressure type offer certain advantages over mechanical seed meters, they have certain limitations of their own which may prove to be a significant disadvantage for various applications. Because the seeds are held in place on the rotating disk or other movable member by differential pressure resulting from positive pressure in the chamber, it is usually necessary that the air flow be directed through the seed mass to aid in the depositing of individual seeds on the disk. The air flow has been found to interfere with the orderly delivery of seeds down to the disk, so that even a very high pressure differential will not necessarily guarantee the avoidance of seed doubles or voids at the various apertures in the disk. In positive pressure systems, the seed hopper must be sealed to maintain pressure. If for any reason the hopper lid comes off or the hopper otherwise becomes unsealed, the seed meter will not function.
Vacuum seed meters have been found to overcome some of the problems in the positive pressure seed meters. In vacuum seed meters a vacuum source is typically coupled to a separate chamber on the opposite side of a seed disk from the seed mass with the vacuum communicating through the apertures in the seed disk to the seed mass. Because the pressure differential at the seed disk comes from a vacuum source on the opposite side thereof and not from a flow of air at the same side thereof as in the case of the positive pressure type of seed meter, the problems of having to direct an air flow through the seed mass and onto the seed disk are eliminated.
Despite the various advantages of vacuum seed meters over meters of the positive pressure type, presently known vacuum seed meters are not without problems of their own. For one thing a relatively high power vacuum source is typically required to provide the large pressure differential needed in order to accelerate the seeds to the speed of the rotating seed disk and thereafter hold the seeds on the disk at the apertures in the disk. Because of the difficulty in accelerating the seeds from the mass to the speed of the seed disk for adherence thereto, various mechanical agitating arrangements are sometimes used at the expense of increased complexity in the construction and operation of the seed meter. A further problem which is aggravated when a large pressure differential is present is that of excess seeds being picked up on the seed disk. Because of this tendency, many vacuum seed meters must be equipped with multiple seed eliminating devices or arrangements to insure that only one seed remains at each aperture in the seed disk as the disk reaches the seed discharge and delivery area. Multiple seed eliminating devices must be adjusted from meter to meter across the planter, thereby increasing operator start-up time. A large pressure differential also creates problems in releasing the seeds from the disk and frequently requires the use of seed ejectors or other devices which complicate the design and operation of the seed meter.
A typical example of a conventional vacuum seed meter is provided by U.S. Pat. No. 3,608,787 of Grataloup. The arrangement shown in this patent which includes a perforated seed disk and a vacuum source requires a special plate containing hollows and projections engaging the seed disk to eliminate multiple seeds. In U.S. Pat. No. 3,990,606 of Gugenhan, a drum has a seed plate attached thereto on which seeds are held by vacuum. The arrangement shown therein requires an interruptor device to close each hole at the discharge position while a seed ejecter device engages the outer surface of the plate. German Patent No. 25 17 758 describes a vacuum seed meter which includes an apertured disk and a distributor wheel with a ring of scoops thereon. French Patent No. 2 376 607 shows a vacuum system having a rotating plate with pockets for selecting potato tubers, one by one.
An example of an earlier and somewhat different design of a vacuum meter is provided by U.S. Pat. No. 3,533,535 of Knapp. In the Knapp patent vacuum is used to hold seeds or other objects within clamshell shaped cells communicating with holes in a rotating drum. The surface of the drum which is comprised of elastomeric material is distorted by spring-loaded plungers which project into the holes in the drum to flatten the cells and aid in seed ejection. U.S. Pat. No. 3,434,437 of Mark et al is exemplary of a separate accelerating mechanism for accelerating seeds from a seed mass to the speed of the seed drum. Likewise, in U.S. Pat. No. 2,991,909 of Lamazow a paddled stirrer is employed to agitate the seeds.
Accordingly, it would be desirable to provide a vacuum seed meter requiring a relatively small pressure differential. It would furthermore be desirable to provide a vacuum seed meter in which seeds are readily accelerated to the speed of and picked up by the seed disk without the need for separate seed agitating and accelerating mechanisms and in the presence of a relatively small air pressure differential. It would be of still further advantage to provide a vacuum seed meter in which the problem of seed doubling or the picking up of excess seeds is minimized. It would be of still further advantage to provide a vacuum seed meter in which seeds held to a seed disk by vacuum are readily and reliably released from the seed disk without the need for complicated release mechanisms.